In fields such as a decorative part for a vehicle and a housing for an electrical product, there is an increasing demand for a deep-tone jet-black appearance from the viewpoints of design and the like. Although a jet black color can be obtained in a black plating layer according to cobalt chromium plating or the like (Patent Document 1), the black plating layer is poor in corrosion resistance.
Thus, a chromate film has been formed on the black plating layer by chromate treatment using hexavalent chromium for improvement in corrosion resistance. Consequently, although a corrosion resistance performance can be ensured, as the counteraction, there has been the problem that a hexavalent chromium component contained in the chromate film develops a strong yellow color, so that a jet black color of the black plating layer looks yellowish when the black plating layer is viewed through the chromate film.